Many hot process streams in refineries are cooled to remove polar contaminants such as H2S and NH3. Removal of these contaminants is important as downstream processes are typically both sulfur (S) and nitrogen (N) sensitive. The current processes for S and N removal are low temperature processes. Currently, there are no high temperature commercial processes for separating polar contaminants (such as H2S and NH3) available. H2S is usually removed by an absorption process using amines, methanol, etc. NH3 is usually removed from the process stream with a water wash. After the removal of the contaminants and before further processing, the process streams must be reheated to elevated temperatures. This cooling and subsequent reheating of process streams, however, results in a significant heat loss and increases the amount of energy required for processing the streams.
FIG. 1 illustrates a current process for removing contaminants such as H2S and NH3 from a process stream. The hydrocarbon stream passes from a hydrotreater 11 at a temperature of approximately 600° F. Before the stream can be processed in a reformer 14, the stream is cooled in one or more heat exchangers. The stream is cooled from 600° F. to 80° F.-100° F. In flash drum or vessel 12, a portion of H2S, NH3 and other lighter components are removed from the remaining heavier components in the process stream. The process stream is then fed to a stripper 13 to substantially remove the remaining portion of H2S and NH3 such that the appropriate levels remain in the process stream (e.g., less than 2 PPM level) before the process stream can pass to the reformer 14. The contaminants removed in the flash vessel 12 and the stripper 13 can then be fed to other processing equipment 15 for further processing. The process stream that is free of contaminants (H2S and NH3) is then reheated to a temperature of 950-1000° F. for processing in reformer 14. This prior art process is inefficient because the process stream must be cooled and subsequently reheated. This results in a significant heat loss even with heat integration, where the withdrawn heat is used to heat other process streams.
There is a need for a process to remove S and N contaminants at elevated temperatures that does not require the significant cooling of the process stream such that heat loss can be prevented and the overall process can be made more energy efficient.